// rem单位换算：定位75，只是为了方便计算 750px-75,640-64,1080px-108
$vm_fontsize: 75;
@function rem($px) {
  @return ($px/$vm_fontsize) * 1rem;
}
$vm_design: 750;
html {
  font-size: ($vm_fontsize/($vm_design/2)) * 100vw;
  @media screen and (max-width: 320px) {
    font-size: 64px;
  }
  @media screen and (min-width: 540px) {
    font-size: 108px;
  }
}
// body也要增加限制
body {
  max-width: 540px;
  min-width: 320px;
}
